import sys
from PyQt5.QtWidgets import *
app=QApplication(sys.argv)
win=QMainWindow()
win.setWindowTitle("QSS")
win.resize(300,500)
win.setObjectName('main')
#win.setStyleSheet("#main{border-image:url(panda.jpg);}")
win.setStyleSheet("#main{background-color:red}")
win.show()
sys.exit(app.exec_())